1. Field of the Invention
This invention relates to a method of preparing ceramic microspheres, more particularly to a method of enabling substantial reduction of equipment size and preparation of microspheres even with ceramics which cannot be transformed into sol.
2. Description of the Related Art
Ceramic microspheres are fine, spherical particles. When used as fillers dispersed in other media, they enable a high filling degree because of the narrow space between particles. When used as sintered bodies formed into various shapes, shaping is easy because of the excellent flow property.
In the known method for preparing ceramic microspheres, the sol of ceramic materials is dropped into a single kind of liquid to form spherical shapes. However this method has a problem, i.e., the need for a long dropping height from the liquid level in order to obtain true spheres, resulting in a large size of the equipment. As a method to solve these problems, Japanese Unexamined Published Patent Application No. 57-84731 discloses the steps of dropping the colloidal sol of ceramic materials into a solution consisting of two layers; a high boiling point liquid which has lower specific gravity than the sol and which is immiscible with water and a liquid with a higher specific gravity than the sol so as to make the spheres and subjecting the resultant product to drying and calcination. This method is capable of making true spheres at a short dropping height from the liquid level, and consequently enables preparation of ceramic microspheres by means of small-sized equipment.
However, the ceramic material for this method is limited to material transformable into colloidal sol. This method cannot be used for ceramic materials not transformable into sol, namely those whose solid particles easily precipitate when dispersed in a liquid.
Also, in this method, the sol dispersed in the high boiling point liquid first must completely gelatinize on the boundary surface of the two liquids before they fall in the lower layer liquid to make the spherical particles. Therefore, the dispersed sol tends to stagnate on the boundary surface of the two liquids, this is troublesome in that the dropped quantity of the sol must be controlled according to the quantity of the spherical particles formed.